The most common and most likely answer to this crossword clue is the 9 letter word FOOLHARDY
I've seen this crossword clue in The Sunday Telegraph
F
O
O
L
H
A
R
D
Y
More clues leading to the result FOOLHARDY
- Reckless kid able to get through the winter
- Sweet member of comic duo is reckless
- Rash caused by rough, dry loofah
- Reckless to hoodwink Nelson’s mate
- Rings Doctor Young at first after new loofah causes rash
- Reckless kid has difficult year
- Pudding put in front of author? That’s not wise
- Daring way to get Hydra
Buddy explains!
The straight part
We know that "That’s not wise" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case that’s not wise = foolhardy.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does FOOLHARDY mean?
FOOLHARDY adjective- Marked by unthinking recklessness with disregard for danger; boldly rash; hotheaded.